Which I want to replace with a programmable thermostat, A siemens RDJ10-GB, to take over the timer that's on the boiler, primarily because the boiler timer can't help with setting automatically a separate night time temperature. It requires 3 feeds as standard, LX, L1 and L2.

At the other end of the wiring, at the Powermax 155x boiler (I know, I know!), it looks like this:

The white cabling at the bottom is the feed from the thermostat.

The fitting instructions from the installation booklet for the boiler:

I'd appreciate if someone could help me out, all I want to know is which wires currently in use would be the ones I need to use with the new thermostat, ie. the LX, L1, L2. Also, I may have to do some wiring at the boiler end.

If my assumptions above are correct, you should find 230V between red and blue, and should find continuity between red and yellow when the thermostat is operational (i.e. demanding the boiler to be on) and open circuit when it's upto temperature.

On my boiler controller, would I leave it on the 24hrs setting, so that the boiler will only be controlled by the room thermostat?

currently the switch on the left is on the 'I' 'Timed' setting (different from in the pic, I was fiddling to see what worked) and now the room controller works as it should, but doesn't this mean that the hot water is on continuously as well, or is that not an issue?

To carry on from my previous post, the instructions I've posted earlier mention some wire arrangements at the boiler, would I need to do this?

thanks
valmiki

[edit] just rang the Potterton helpline, looks like I don't need to do anything. The 155x has a cylinder but it is only used for CH, hot water is on demand only. Cheers valmiki.

Glad it all went to plan

Your wiring could certainly be simplified, as I mentioned before you seem to have 5 core cable leaving the boiler and only 2 wires are needed at the thermostat... but if it's all working and you don't want to start ripping wires out and replacing them then I would leave as is.

The wiring as you've connected it is as it should be, your configuration falls under paragraph 5. i.e. you have a clock type thermostat connected to pins 27 and 28 in the boiler.

On my boiler controller, would I leave it on the 24hrs setting, so that the boiler will only be controlled by the room thermostat?

currently the switch on the left is on the 'I' 'Timed' setting (different from in the pic, I was fiddling to see what worked) and now the room controller works as it should, but doesn't this mean that the hot water is on continuously as well, or is that not an issue?

Looking at the built in programmer at your boiler, there appears to be two channels, one marked (HW) hot water and the other (CH) central heating. Why not set the CH to 24 hrs and use the HW time settings as before?

Depending on the design of your plumbing, you may find that you will need to have the HW set 'on' at the times you want the central heating on for it to work anyway, but even if you do, at least the HW won't be on 24/7

Interesting, the Danfoss controller looks full of features but is twice the price I paid for the Siemens, however I'll take a closer look just in case - if it looks worth it I may buy it and flog the Siemens one on fleabay.

stem, this was one of the reasons why I asked my questions. There are two channels for HW and CH but on the programmer the CH 'forces' the HW to the same setting. For example, I can have HW and CH both on auto (timer) but if I change the CH to 24hrs it will also change the HW to 24hrs, if that makes sense? With the CH on 24hrs I can't change the HW to anything else.

This was why I though initially that I'd have to adjust some wires at the boiler, but the bloke on the helpline was adamant that the HW on these boilers is on demand only - but if that's the case why would it have a separate channel for programming?

Guess you guys know more about this than I do, I'm just glad that the bloke on the phone didn't want to check I was corgi-registered, etc.